1. Field of the Invention
This invention relates to a printing process using lithographic plates which are made from toned amplitude modulated magnetic images.
2. Background Description
Most commercial printing plates for lithography are made by preparing 150 line/in halftone transparencies from continuous tone images and using the transparency to expose an oleophilic photosensitive layer on a water receptive substrate. The lithoplate is then mounted on a lithopress where ink will be applied and will adhere to the oleophilic regions and water will adhere to the hydrophilic regions. The ink film thickness is about the same for large dots as for small dots, since lithography is an on-off process.
R. B. Atkinson and S. G. Ellis, U.S. Pat. No. 2,826,634 describe a method for reproducing pictures which involves forming an amplitude modulated latent magnetic image using anhysteretic recording, toning said image with magnetic particles and transferring the magnetic particles to a final support, in particular paper or coated paper, using pressure or combinations of pressure and a dampened support. If additional copies are desired, the latent magnetic image is retoned and the toner transferred to another final support. No mention is made of magnetic recording distortions resulting from having recording tracks too close together.
EPO Publication No. 0.004,383 discloses a resist process comprising decorating a latent magnetic image with coalescible magnetic toner particles to form a toner image, bringing the toner image into momentary contact under pressure with a heated substrate surface to tackify the toner particles forming said image which are in contact with the heated substrate surface thereby causing said particles to adhere to said heated substrate. The thus transferred particles form an image of at least partially coalesced toner particles on said heated surface. Further coalescing of said toner particle image may be necessary to form an impervious image. The area of said surface not covered by the resultant resist image is treated to make it hydrophilic or hydrophobic, opposite that of said resist image, so as to form a planographic printing plate.
We know of no discussions of the effect of line-to-line interactions on the resultant visual image obtained for a magnetically recorded image which is subsequently developed by applying a magnetic toner. A. van Herk, IEEE Transactions of Magnetics, Mag-13, 1021 (1977), has calculated the amplitude of the read crosstalk signal as a function of the field strength of the recording field and the head-to-recording medium distance for signals recorded and read by magnetic heads and uses the results as a basis for suggesting line-to-line spacings for this type of situation.